Railway signaling



April 23,1929, y 1 v, LEWIS y 1,710,499

RAILWAY SIGNALING original Filed oct. s, 1916 4 Sheef'sheeg 1.

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April 23, 1929. l.. v.v LEwls RAILWAY SIGNALING original Filed oct. s,1916 4 sheets-sheet INVENTOR /M i N ...UE

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RAILWAY SIGNALING Org'i'nal Filed Oct, 5, 1916 4 Sheets-Sheet 3 FIG-[4INVENTOR wlTNEssES April 23, 1929. 1 \ll. LEWIS RAILWAY SIGNALING 4Sheets-Sheet original Filed oct. s, 191e Lilla m R R k A RR R. R

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Panarea Apr. 23,1929.

UNITED STATES PATENT. oEr-icE LLOYD V. LEWIS, OF EDGEWOOD BOROUGH,PENNSYLVANIA, ASSIGNOR TO UNION SWITCH & SIGN AL COMPANY, 0I SWISSVALE,

PENNSYLVANIA.

' RAILWAY sIGNALINa Application led October 3, 1916, Scrial'IN'o.123,493. Renewed October 12, 1928.

My invention relates to railway signaling. I shall describe severalforms of'apparatus and l circuits embodying my invention and then pointout the novel features thereoflv 1n 5. claims.

-In the accompanying drawings Fig. 1 is a diagrammatic view showing oneform and arrangement of trackway apparatus and circuits embodying myinvention. Fig. 2 1s a diagrammatic view showing onel forml andarrangement of vehicle carried circuits and apparatus lembodying in yinvention and adapted for use in connection with the trackway circuit-sshown in Fig.1. Fig. 3 is a r respectively.

" diagrammatic view showing a modification of the trackway apparatus andcircuits shown in Fig. 1. Fig. 4 is a diagrammatic view showing amodification ofthe vehiclecarried apparatus and circuits shown in Fig.2, the apparatus and circuitsbcing adapt-ed yfor use i-n connection withthc circuits shown in Fig. 3. Figs. '5 and 6 are diagrammatic viewsshowing modifications of the trackway apparatus and circuits shown inFigs. 1 and 3 and also embodying my invention.

Similar reference ycharacters refer to similar parts in each oftheseveral views.'

Referring first to Fig. 1, reference char.

acters 1 and 2 designate the track rails of a stretch of railway trackA-B, which lrails are electrically continuous throughout the length ofthe stretcli.` G' and G' are generators of alternating signaling-currents of frequencies which I shall designate g and g',

y These frequencies are preferably higher than those now in commercialuse, but lowen than the order of frequencies now in general use inwireless telegraph practice. The generators G and G 'are connectedrespectively to transmission lines N and N parallel to the railwayytrack. .Current from line N is fed to the track rails at a by means of atransformer 6 connected to the line N by wires 3 and 4. The secondarycircuit of this -transformer comprises a conresonance for. current offrequency g. The:

secondary coil of transformer 8 is connected in series Awith a condenser9 to' the track rails 1 and 2, the condenser 9 having such capacity thatwhen the railsare bridged by v a car or train a considerable distancefrom point a the secondary circuit of transformer 8 is-resonantatfrequency The above de,

The connection from line N to the track rails I at .o comprises similara paratus, similarly adjusted to resonance or current of the samefrequency g. Line N vis connected in similar manner to the track railsat points b and d, the connecting apparatus being ad- ]usted toresonance for the current from gen'l erator G. vThe points at which lineN is connected to the track rails alternate with the points at which theline N is connected to the rails, as shown on the drawing, so thatadjacent points of connection with the track rails are supplied withcurrents differing 1n frequency.

The signaling currents thus supplied to the rails 'flow along the railsto a railway the wheels and axles of the car or train. If

there i-s a car or train 'V on the track lbetween band c,.as shown onFig.' 1, all currents that PENNSYLVANIA, A CORPORATION OF pedance to theiow of current from generare supplied to the Irails at points to theright' of the car or. train are short-circuited by the car axles,whereby they are prevented from owing' beyond the car or train into therails to the left thereof. Similarly, the currents in the rails to theleft of the car or train are short-circuited by the car axles so thatthey cannot flow into the rails on the right of the car 0r train.- vEach c ar or train is provided with control apparatus responsive' to thecurrents inthel trackrails immediately in advance of the car or train,which apparatus I shall now describe. Referring to Fig. 2, this controlapparatus comprises a coil 10 fixed to the'v vvehicle V in front of thefront axle and in inductive relation to the front axle and to the trackrails 1' and 2 immediately in advance of such axle. A condenser 41'1 isconnected in series with coil 10, the inductance of the'coil and thecapacity of the condenser being of such relative values that the circuitformed by the condenser and the coil is resonantfor the mean of thefrequencies g and g. When, therefore', current of either frequency ispresent in the t 'ack rails it will induce in circuit m alternatingcurrent of the corresponding frequency. Circuit a' is connected by wires14 and 15 to the grid 16 and the filament 17 of a vacuum tube amplifier'P, a device now well known in the art. Briefly, described this amplifiercomprises a vacuum bulb 18 enclosing a plate 20, the grid 16 and thefilament 17 above referred to, which filament is constantly heated to.ineandescence by current from a battery 19. A continuous current issent through the amplifier by means of a battery 21, the negativeterminal of which is connected to the filament 17 and nthe positiveterminal of which is connected to the plate 20, the circuit, which lshall designate y being in detail: from battery'21, through transformersT and T', wire 23, plate 20, filament 17, to battery 21. The grid 16 isinterposed between plate 20 and filament 17, and when the voltagebetween the grid and the filament is caused to vary, the current in thecircuit just traced fluctuates in accordance with the variations in thevoltage. 1When an alternating voltage is impressed between grid 16v andfilament 17, as for example, by current in circuit a", the current frombattery 21 is caused to pulsate in harmony with the frequency of thealternating voltage in circuit the variations of the current in circuity being of much greater-.magnitude than the amplitude of the current incircuit The inductance of the transformers T and T is balanced by acondenser 25 which has such capacity that the local circuit comprisingthe two transformers and the condenser in series is resonant at theymean of the fre'- quencies g and g.

The secondary circuits of transformers T and T comprise, respectively,relays S and S connected in series with condensers 26 and 26, thecapacities of vwhich condensers are such that the circuits comprisingrelays S and S are respectively resonant at frequencies g and g. When,therefore, there is current of frequency g in circuit y the relay S isenergized, and when there is current of frequency g. in circuit y therelay S is energized. As explained hereinbefore, the current in circuity depends -upon the currents induced in circuit .fr by the signalingcurrents in track rails 1 and 2 in front of the car or train, henceit isclear that current in the track rails of frequency g causes energizationof relay S and that current in the rails of frequency g causesenergization of relay S". Relay S will not respond however to current offrequency g', and likewise relay S will not respond to current offrequency g; and to insure this selection the imanes two relays may beso constructed as to be selectively responsive to the currents to whichthey are intended to respond.v

Relays S and S may govern suitable signaling apparatus, or speedcontrolling apparatus, or both, on the vehicle, as I shall now describe.Reference characters LG, LY, and LR designate signal lamps comprised inacab signal F, which lamps indicate respectively, when illuminated,proceed, proceed with caution, and stop. The green lamp LG isilluminated only when both relays S and S are energized, theeircuitbeing: from battery 3G, through wire 31, front contact 32 of relay S,wire 33, front contact 34 of relay S, wire 35, green lamp Cr, Wires 36and 37 to battery 30. The yellow lamp LY is illuminated when only one ofthe relays S or S is energized and the other is de-energized; whenrelayy S is the one' which is energized, the circuit for lamp LY is frombattery 30, through wire 31, front contact 32 of relay S, wire 33, backcontact 34 of relay S, wire 40, lamp LY, wires 36 and 37 to battery 30;when on the other hand relay S is the one which is energized, thecircuit for lamp LY is from battery 30, through wire 31, back contact ofrelay S, wire 38, front contact 39 of relay S, wire 40, lamp LY, wires36 and 37 to battery 30. When both relays S and S are de-energized, lamLR is illuminated by current in the following circuit: from battery 30,through wire 31, back contact of relay S, wire 38, back contact 39 ofrelay S, wire 41, lamp L, wires 36 and 37 to battery 30. It is clearfrom the foregoing, that when both relays S and S are energized, the cabsignal gives` the proceed indication; when only one relay is energized,the signal gives the caution indication, and when both relays arede-energized, the signal gives the stop indication.

To enforce observance of these signals, suitable automatic vehiclegoverning means may be provided for use in connection with llt) relays Sand S". In the form here shown this means comprises' a centrifugaldevice 44 operatively connected with an axle of the vehicle. Thiscentrifugal device controls a magnet 42, which magnet governs a valve 43in the fluid pressure brake. system of the vehicle, in such manner thatthe brakes are applied when the magnet is deenergized. The arms of thecentrifugal device are connected at one end to a shaft 45 bearing acontact sleeve 45, so 4that the spread of the fly balls due to movementof the car or train causesthe cont-act sleeve 45a to move to the right.The contact sleeve -coacts with three'pairs of contact fingers 46 and46a, 47 and 47, 48 and 48a, in such manner that all three pairs ofcontact fingers are bridged by the contact sleeve when Ythe speed of thecar ortrain is low, as, for example, miles per hour and less. Above thisspeed the sleeve 45 is drawn out of' engagement with the rst pair offingers 46 and 46a, remaining however, in engagement with the other twountil the speed of the car orptrain reaches an intermediate value suolias miles per hour. Above this includes the right hand pair of contactfingers 48 and 48, the circuit being' from battery 30, through frontcontact 50 of relay S, wire 51, front contact 52 of relay S, wire 53,contact finger 48, sleeve a, contact finger 48a, wire 54, magnet 42,Wires 55 and 37 to battery 30. When only one of the magnets S or S isenergized, the circuit for magnet 42 includes the middle pairof contactfingers47 and 47; when rela S is energized and relay S de-energize thecircuit is :troml battery '30 through front con- `tact of relay S, Wire5,1, back contact 52 of relay S', Wlre 56, contact finger 47, contactsleeve 45a, contact finger 47, wire- 54, brake magnet 42, wires 55 and37 to battery .30; when relay S is energized instead of relay S, thecircuit is the same as traced above except that it passes through theback contact 50 of relay S, wire 57, and front contact 58 of relay S towire. 56. When neither relay S nor S is energized, the circuit formagnet 42 includes the left hand pair of contact fingers 46 and 46a, thecircuit in detail being from battery 3() through wire 59, contact finger46, contact sleeve 45a, contact linger 46, wire 54, magnet 42, wires 55and 37 to battery 30. y It is clear therefore, that when both relays ASand S are energized the speed of the car or train is limited only to 60miles per hour. When,l 1owever, only one of these relays'. is energized,the speed limi't'is reduced to 30 miles per hour, .and when both relaysS and S are de-energized, the speed is limited to 5 miles per hour. Itis understood, however, that the apparatus herein shown foraccomplishing this control of' the speed of the car or train by relays Sand S is merely illustrative, and that any other suitable appara-v v tusmay be employed in the practice of my invention.

-It will now be clear that when a car orl train equipped lwith theapparatus shown in F ig. 2 proceeds over track rails in which bothsignaling currents are flowing, the cab signal gives a proceedindication and the speed of the car or train is limited only 'to 6()miles per hour; when'the car or train proceeds over track rails in whichonly one of the signaling currents is fiowing, the cab signal indicatesproceed with caution and the brake control apparatus limits the speed to30 miles per hour; and when the car or train enters upon track rails inwhich neither of the signaling currents is flowing,

the cab signal changes to stop yand thel brake control apparatus limitsthe speed to 5 miles per hour or less.

From the above description ot'l apparatus the operation of the signalingsystem will be easily understood. For a brief explanation I shall assumethat in Fig. 1 there is` a car or train V on the track between points band c and that lanother car or train V approaching from the left, thelatter car or train being equipped with the apparatus shown in Fig. 2.IWhile vehicle V is to the left of point a both signaling currents arepresent in the track rails in advance of the vehicle, so that thecabsignal indicates proceed and the speed of' the vehicle is limitedonly to 60 miles per hour, as I have previously described. When thevehicle passes beyond point however, only one of the signaling currentsis present in the track rails, namely, current from generator G',consequently the cab signal changes its indication to caution and unlessthe speed has -been reduced to 30 miles per hour or less, the

ICS

until the vehicleV is, reached or the 'signal indication is changed. Itthe engineer fails to comply with this rule, the brakes will be appliedautomatically until the speed ofthe Ulf) train is less'than 5 milesvperhour. If now the first train V moves to the right beyond c, signalingcurrent from generator G again fiows in the track rails in advance ofthe car or train V `so that the engineer of the latter train receives aproceed with cau'- tion signalin the cab. At the same time.

the speed limit imposed on the car or train is raised, allowing the caror train to proceed at a speed of 30 miles per hour.

Referring now toFig. 3, the signaling system here shown is similar tothe system previously described, but it comprises four generators G',-G2, G3 and G4, generating currents of four distinct frequencies, whichfrequencies I shall designate g, g2, g3 and g4, respectively. In the.arrangement here shown, all of the generators are connected to onetransmission line N, which line is connected to thetrack rails at a, b,c, etc.,

by means of intermediate circuits, each of which circuits is resonantfor one of the frequencies of current in line N, so that only current.of the one frequency can enter the track rails at each of the saidpoints of connection. For example, at point a the rails are suppliedwith current by a transformer 6T whose secondary is connected with therails and whose primary is connected with the swfondary of anothertransformer 69, the primary of the latter being connected with thetransmission line N. The circuit including the rails and the secondaryof transformer 67 is tuned to resonance at frequency g by a condenser68, and the circuit including the secondary of 69 and the primary of 67is similarly tuned to the same frequency by a condenser 70. Tn thismanner the rails are furnished at ai With current of frequency g', at bwith current of frequency g2, etc., currents of the various frequenciesbeing supplied to the track rails in rotation as indicated by lettersg1, g2, etc. on

ythe drawing. lVhen, therefore, in Fig. 4

the cars or trains V and V areseparated by four or more trackconnections, the track rails in front of car or train V are energized byfour signaling currents. When the second car or train V approaches thefirst car or train V until they are separated by only three trackconnections, the rails between them are energized by only threesignaling currents. It is clear, therefore, that, as the car or train Vapproaches closer to car or train V, the track rails between the cars ortrains carry fewer signaling currents, until the rails are completelyde-energized as the second car or train V passes the last trackconnection behind vthe first car or train V. It may be said, therefore,that the number of signaling currents in the track rails in front of acar or train depends upon the distance to the next car or train'ahead.

Referring now to Fig. 4, the apparatus on the. ear or train for use inconnection'with the trackway circuits shown in Fig. 3 is similar to theapparat-us shown in Fig. 2 previously described. The circuit is tuned toresonance at the mean of the four frequencies g', g2, g3 and g4. Thecircuit y, however, comprises in seriesthe primary windings of fourtransformers T, T2, T3, T4, having secondary circuits comprising cabrelays'S. S2, S3 and S4, respectively, which circuits are adjusted toresonance for frequencies g', g2, g3 and g4, respectively. From thedescription of Fig. 2 it is clear that the relays S', S2, S3, and S4,respond respectively to signaling current in the track rails of thefrequencies g', g2, g3 and g4.

These relays control, as in Fig. 2, af cab signal F, Whichas here showncomprises five lamps, the faces of which are marked respectively Withnumerals 60 45, 25, l() and 5, which numerals designate the permissiblespeed of the car or train in miles per hour. `When all of the cab relaysare fle-energized, the lowest lamp, marked 5, is illuminated, indicatingthat the speed of the car or train must not exceed 5 miles per hour..Vhen any one of the cab relays is energized, this lamp is extinguishedand the next higher lamp is illuminated, indicating that the speed maybe raised to l0 miles per hour. In this manner, as the number ofenergized relays increases, the speed limit indicated by the lamps israised in steps to the maximum of miles per hour at which time all fourrelays are energized. These speed limits may be enforced, if desired, bya governor 44 controlling contacts in the circuits of the magnet 42, thecontrol of these circuits being similar to the control shown in Fig. Qand explained hereinbefore.

The operation of this signaling syst-em is similar to the operation ofthe system shown in Figs. l and 2. Referring again to Fig. 3, it isapparent that the coil 10 on car or train V receives signaling currentsof four frequencies as it approaches car or train V, until train Vreaches the track connection `designated c. With four signaling currentsin the track rails the four cab relays S', S2, S3 and St are energizedso that the cab signal indicates the highest speed limit of miles anhour and the governor limits the speed of the car or train accordingly.However, as the car or tra-in V passes point c, the track rails in frontof the car or train are energized by only three of the signalingcurrents, namely, those currents having frcquencies g4, g', and g2. As aresult, the relay S3 inthe cab is der-energized, leaving only three ofthe cab relays closed, so that the signal G changes its speed limitindication to 45 miles per hour and the governor 44 becomes effective toenforce this speed limit as explained hereinbefore. As the car or trainV proceeds still further and passes point d, signaling current of thefrequency g4 is also shunted from the track rails in front of the ear ortrain so that relay S4 in the cab becomes cle-energized. Only relays Sand S2 are now closed, so that the eab signal indicates a speed limit of25 miles per hour and the governor becomes effective to enforce thisspeed limit. As the car or ytrain passes point e, signaling current ofonly one frequency, namely, g2 energizes the track rails in front of thecar or train so that only relay S2 in the cab is energized, whichresults in a speed limit of 10 miles per hour. As the car or trainpasses point f, it enters upon fle-energized track rails so that none ofthe relays in the cab are closed and the cab signal changes its speedlimit indication to 5 miles per hour, which limit is enforced bythegovernor, as previously explained. Tt Will be seen that thisr signalingsystem differs' from the one previously described .while the caror trainis running on this down grade I supply to the track rails of thissection only two frequencies of sig.- naling currents so that only twoof the cab relays can be energizedeven when there is no other car ortrain ahead, whereby the car or train is automatically prevented from'assuming a higher speed than 25 miles per hour in the manner explainedhereinbefore. As shown in Fig. .5, the frequencies g and g2 arenotsupplied to the rails on the down grade, andthey are prevented fromflowing into this Isection of the rails by lshunts 65 and 66 connectedbetween the rails adjacent II. The shunt 65 comprises an inductance anda condenser resonant for frequency g', so that current of this frequencyin the rails to the right of the shunt is short-circuited and preventedfrom flowing into the rails extending to the left of the shunt. In thesame manner the current of frequency g2 lis prevented from` flowing pastthe shunt 66 which is resonant at frequency g2. When, therefore, a caror train equipped with sign al and speedcontrolapparatus, as shown anddescribed in Fig. 4, approaches'the down grade extending from I to II,traveling in the direction of the arrow, the coil 10 thereon receivesall four signaling currents upto the point designated lo so that thespeed is limited only to miles per hour. After passing vthis point,however, the car or train short-circuits the current of frequency g'supplied at c so that this lcurrent cannot flow into the track railspreceding "the car or train. Current of frequencyg is not supplied tothe track rails within the limits of the down gradesection, aspreviously mentioned, and cannot flow into these rails from the railsbeyond the lower end of the grade because of the resonant shunt 65. Thetrack rails in frontof the car or train are therefore energized only bysignaling currents of frequencies g, g3 and g4, so that only three cabrelays are energized and the speed limit is reduced to 45 miles perhour, as hereinbefore explained. As the car or train passes point 1, itshunts out current of frequency 'g2 from the trackrails ahead of4 `thecar o r train so that the speed limit is automatically reduced to 25miles .perhour, as hereinbefore explained. Signaling currents offrequencies g3 and gv4 are supplied tothe track ralls on fthe downgrade, permitting the car. or -train to proceed down the grade at 25miles per hour, unless there is another car or tram in advance, in whichcase the first-mentloned -car -or train must slow down rst-to 10 lmilesy is connected between the track rails.

per hour and then to 5 miles per hour in the manner which- I haveexplained hereinbefore. Assuming that the track is unoccupied. the caror train proceeds at 25`miles per hour to' the point at which theshrlllllt rails beyond this point are energized by current of frequencyg supplied at 0 so thatA the speed limit is changed to 45 miles perhour. As the car or train passes shunt 66 it enters on track railsenergized by signaling currents of all four frequencies, so that thespeed limit is raised to 60 miles per hour permitting the car or trainto resume normal speed.

.In similar manner a reduced speed limit may be imposed on cars ortrains when passing over curves, switches or tunnels.

Referring now to Fig. 6, reference character Q designates a railwayswitch in a section of track IV-VI. When the switchis in its normalposition, traiic passing over the switch in the direction of the arrowcontinues on the straight or high speed route, Whereas when the switchis in its reversed position, traiiic passing over the switch is divertedinto a branch track 110, which I will term a medium speed route. Forpurposes of description `I shall assume that the maximum safe speed onthe high speed route is' 60 miles per hour, whereas on the mediumspeedroute it is 25 miles per hour. Reference character K designates asignal stationed adjacent the trackway, which signal comprises twosemaphore arms 108 and 104. These arms are fnormally in the horizontalposition, indicating stop. When arm 104 is raised to the verticalposition it indicates that switch Q, is normal, and when arm 103 israised to the vertical position it indicates that switch Q is reversed.

I have omitted from the drawing the eircuits for the control of signalK, these circuits being irrelevant to my invention. It need here bementioned only that a track circuit comprising the track rails from IV`and, VI enters into the controlof signal K through a track relay 106,the length of the track circuit being dened by insulated joints 112 inrail 2. The track circuit is supplied by atransformer 111 adjacent pointVI l 'an alternator U. The indications of signal K are'repeated by adistant signal Ka located in the rear of signal K, the arms 101 and102of signal Ka corresponding respectively to semaphores 104 and 103 ofsignal K. Signal Ka is also controlled by a track circuit extending frompoint III to point IV, which circuit comprises a track relay 107,energized also from the low frequency source U.

For the purpose of repeating the; indications of signal Ka and K in thecab of a car ortrain', and in order to automatically enforce observanceof ,these signals, I provide my hereinbefore described high frequencysignaling system suitably modified, as I shall now describe. Theapparatus on the car or train may be the same as that shown in Fig. 4.'Ihe transmission line'N energized by generators G, G2, G3 and G4,supplies signaling currents to thc track rails, in somewhat the samemanner as in Fig. 3, ,the frequency supplied to the track rails beingindicated by the same letters as before at each point of connection. Itshould here be noted that the insulated joints 112 in rail 2 prevent thchigh frequency signaling currents supplied to the track rails within theinsulated sections from flowing beyond the limits thereof. For example,with the arrangement of apparatus thus far described, current offrequency y supplied at 123vto the track rails in section III-IV canno-tflow to the rails extending to the left of point III because of joint112 in rail 2. To pass this current around the said joint I provide ashunt 119 connected to the ends of rail 2 abutting said joint, whichshunt is resonant for frequency g,so that currents of the otherfrequencies cannot flow through this shunt in appreciable quantities.

A car or train V traveling` in the direction of the arrow will receiveat 120 current of frequency g as Well as currents of frequencies g2, g3and gt, so that the car or train may proceed at 60 miles per hour. Whenthe ear or train passes point 120 it will, however, receive only threeof the said currents i. e. g', g and g3, unless the frequency g4 issupplied to the rails through a transformer 124, whose connection to theline L is controlled by the relay 107, the control being such thatcurrent flows to the transformer only when thesection III-IV isunoccupied. In similar manner current of frequency g3 is supplied to thesaid rails by a transformer 125, similarly controlled by relay 107. Inthis manner the car or train may proceed at full speed to the entranceof section III-IV except when said section is occupied, in which casethe speed of the car or train is reduced automatically.

Assuming now that the section III- IV is unoccupied and that signal K atthe entrance to the next section is at stop, 'the car or train onentering section III-IV receives only three signaling currents g', g'1vand g3 supplied to the track rails at 123, 120 and 127, so that thespeed of the car or train is reduced to 45 miles per hour. As the car ortrain passes point 123 its speed is reduced to 25 miles per hour, atpoint 126 it is limited to 10 miles per hour, and at 127 it is limitedto 5 miles per hour, all in the manner hereinbefore explained.

.VVhen, on the other hand, signal K indicates proceed at full speed, i.e. when semaphore arm 104 is in the vertical position, all foursignaling currents are supplied to the rails of section III-IV adjacentpoint IV through transformers 130, 131, 132 and 133, respectively, whichtransformers are controlled through contacts 104, 104, 104, 104,governed by arm 104 of sig-v nal K, the contacts being closed or openaccording as blade 104 is horizontal or vertical'. In this manner thetrain receives all four signaling currents as it approaches signal K sothat it may pass this signal at full speed, in accordance with theindication of the signal.

When, however, the signal K indicates proceed at medium speed, blade 103being vertical and blade 104 horizontal, only currents of frequencies gand g2v are supplied to the track'rail's at point IV throughtransformers 130v and 131 governed by'contacts l 1032L and 103D,operated by signal blade 103. In this case the car or train receives allfour frequencies of current only -up to point 126 in the section III-IV..After passing this point only three currents are transmitted to the caror train and the speed is reduced to 45 miles per hour. .At 127 thespeed is reduced to 25 miles per hour, thus insuring a safe medium speedwhen the car or train passes signal K.

The control of the car or train after it passes signal K is the same ashereinbefore described; in connection with Fig. 3; I have omitted thecircuits and apparatus for the control thereof to avoid unnecessarycomplication of the drawing.

Although I have herein shown and described but several forms ofapparatus and circuits embodying my invention, it is understood thatvarious changes and modifications may be made therein within the scopeof the appended claims without departing from the spirit and scope of myinvention. I

Having thus described my invention, what I claim is: f

1. A stretch of railwa track, a plurality of sources'of current di eringin frequency connected to the rails of said track, and a shunt resonantat one of said frequencies connected between said rails for preventingflow of said current beyond said shunt.

2. In combination, a stretch` of railway track supplied with a pluralityof signaling currents, a portion of said stretch being supplied with alesser number of signaling currents, means for preventing currents notdirectly supplied to the said portion from entering said' portion at oneend, and vehicle-carried controlling means responsive to said signalingcurrents.

3. In combination, a stretch of railway track comprising a portionnecessitating a lower speed than the remainder of the stretch, means forsupplying to said portion one or more signaling currents and forsupplying to the remainder of the stretch a greater number of signalingcurrents, resonant means for preventing the signaling currents notdirectly supplied to the said portion ofthe stretch from entering saidportion, and vehicle-carried governing means 5 responsive to the saidsignaling currents.

4. In combination, a stretch of railway track comprising a portionnecessitating a lower speed than the remainder of the stretch, means forsupplying to the track -10 rails of said portion one or more signalingcurrents and for supplying a greater number of signalin currents to thetrack rails of the remain er of the stretch, resonant shunts connectedbetween said track rails for preventing the How of the signalingcurrents into Said portion and vehicle-carried governing means.responsive to the number of signaling currents supplied to the trackrails in front of the vehicle.

In testimony whereof I aiix my signature.

LLOYD v. LEWIS.

